Effective new palladium catalysts for the Suzuki coupling of various haloxylenes to prepare sterically hindered bi- and triaryls

Several new ortho-alkyl and heteroalkyl substituted aryl and aryl alkyl phosphanes and their palladium complexes have been selectively prepared, characterized and compared as potential catalysts for the Suzuki coupling reaction. The modification of the structures of the palladium complexes were made in search of the best possible catalytic activity. The novel catalysts were subsequently used to synthesize sterically hindered bi- and triaryls by coupling various bulky, unactivated bromoxylenes and chloroxylenes with a range of phenyl boronic acids under microwave irradiation. We showed that under optimized reaction conditions, very good results can be obtained with a selection of the new phosphanes and their mononuclear palladium complexes. (C) 2009 Elsevier B. V. All rights reserved.